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<br />2.3 Principal Flood Problems <br /> <br />Floods in the study area are usually caused by general rainstorms, <br />and cloudburst storms occur from May through September. During <br />this period, warm, moist air masses from the Gulf of Mexico combine <br />with cold and comparatively dry air from the polar regions to cause <br />thunderstorms. Floods resulting from prolonged heavy rainfall over <br />the watershed are characterized by moderate volume and duration. <br />The cloudburst type is a high-intensity, short-duration rainstorm <br />which produces a flood of high peak flow, short duration, and small <br />volume of runoff. <br /> <br />Flood potential also exists from rapid melting of heavy snow cover <br />in late spring and summer. Floodflows resulting form snowmelt are <br />characterized by moderate peaks, large volume, and long duration. <br />Arkansas River peak flow from snowmelt occurs in June and July. <br />This peak flow in combination with rainfall can cause severe <br />flooding. <br /> <br />Detailed information on floods before the turn of the century is <br />very limited. Information on past flooding is based on newspaper <br />accounts and interviews with long-time residents of the area. <br />Large floods have occurred in 1909, 1921, 1932, 1941, 1948, 1949, <br />and 1965. These floods have caused major damage, disrupting <br />highway and railroad traffic and communication services, drowning <br />livestock, and destroying agricultural lands, roads, bridges, and <br />buildings. Several persons have lost their lives and others have <br />been injured (Reference 6). <br /> <br />The flood of June 1921 is considered the most severe flood known in <br />the area. Peak discharges have been estimated by the U.S. <br />Geological Survey (USGS) at 2,760 cubic feet per second (cfs) for <br />Oak Creek and 3,720 cfs for Coal Creek. Floods in 1909 and 1932 <br />were characterized by high-intensity cloudbursts, while the floods <br />in 1941, 1948, 1949, and 1965 were caused by high-intensity <br />cloudbursts coupled with hail-choked runoff channels. <br /> <br />2.4 Flood Protection Measures <br /> <br />There are very few existing flood control structures in the study <br />area that could reduce any flood hazards. In the 1930' s, Coal <br />Creek, in and around the City of Florence, was lined with concrete <br />slabs, grouted in place to form a concrete slopewall lining both <br />sides of the creek. This slopewal1 was capped with a 3-foot <br />floodwall. This channel through the City of Florence, however, is <br />capable of conveying only the minor flood volumes through the City <br />without exceeding the capacity of the channel and bridge structures <br />over the channel. <br /> <br />Various agencies have performed minor channel clearing <br />riprapping along Coal and Oak Creeks, but no extensive <br />control work has been performed since the 1930's. <br /> <br />and <br />flood <br /> <br />4 <br />